22 SCHIZOPHYTA. 



Class 4. Schizophyta, Fission-Algae. 



The individuals are 1 many celled ; the thallus consists in 

 many of a single cell, in others of chains of cells, the cells dividing 

 in only one definite direction (Figs. 18, 21). In certain Fission-Alga? 

 the cell-chain branches (Fig. 30) and a difference between the an- 

 terior and the posterior ends of the chain is marked ; in some, the 

 cells may be united into the form of flat plates by the cell-division 

 taking place in two directions ; and in others into somewhat cubi- 

 cal masses, or rounded lumps of a less decided form, by the divisions 

 taking place in three directions ; or less defined masses may be 

 formed by the divisions taking place in all possible directions. 



The cell- walls rarely contain cellulose, they often swell con- 

 siderably (Figs. 20, 22), and show distinct stratifications, or they 

 are almost completely changed into a mucilaginous mass in which 

 the protoplasts are embedded, e.g. in Nostoc (Fig. 22), and in the 

 "Zoogloea" stage of the Bacteria (Fig. 27). Sexual reproduction 

 is wanting. Vegetative reproduction by division and the separa- 

 tion of the divisional products by the splitting of the cell- wall or 

 its becoming mucilaginous ; among the Nostocacea?, Lyngbyaceie, 

 Scytonemacese, etc., " Hormogonia " are found ; in Ghamcesiphon 

 and others single reproductive akinetesare formed. Many Fission- 

 Alga? conclude the growing period by the formation of resting 

 akinetes or aplanospores. 



The Schizophyta may be divided into 2 families : 



1. SCHIZOPHYCES;. 



2. BACTERIA. 



Family 1. Schizophyceae,* Blue-Green Algse. 

 All the Blue-green Alga? are able to assimilate carbon by means 

 of a colouring material containing chlorophyll (cyanophyll) ; but 

 the chlorophyll in this substance is masked by a blue (phycocyan), 

 or red (phycoerythrin, e.g. in Trichodesmium erythrceum in the Red 

 Sea) colouring matter which may be extracted from them in cold 

 water after death. The colouring matter, in most of them, per- 

 meates the whole of the protoplasm (excepting the cell-nucleus), 

 but in a few (e.g. Glaucocys/is, Phragmonema), slightly developed 

 chromatophores are to be found. Where the cells are united into 

 filaments (cell-chains) a differentiation into apex and base (Rivu- 

 lariacece) may take place, and also between ordinary vegetative 

 cells and heterocysts; these latter cannot divide, and are dis- 



* Myxophyceas, Cyauophycere. 



